Heart failure can occur when the left ventricle of the heart becomes enlarged and dilated as a result of one or more of various etiologies. Initial causes of heart failure can include chronic hypertension, myocardial infarction, mitral valve incompetency, and other dilated cardiomyopathies. With each of these conditions, the heart is forced to overexert itself in order to provide a cardiac output demanded by the body during various demand states. The result can be an enlarged left ventricle.
A dilated or enlarged heart, and particularly a dilated or enlarged left ventricle, can significantly increase tension and stress in heart walls both during diastolic filling and systolic contraction, which contributes to further dilatation or enlargement of chambers of the heart. Prior treatments for heart failure include pharmacological treatments, assist devices such as pumps, and surgical treatments such as heart transplant, dynamic cardiomyoplasty, and Batista partial left ventriculectomy. These prior treatments are described briefly in U.S. Pat. No. 5,961,440, entitled “Heart Wall Tension Reduction Apparatus and Method,” issued on Oct. 5, 1999, the entirety of which is incorporated by reference herein.
A more recent concept for treating heart failure applies one or more splints onto the heart, to reduce myocardial muscular stresses encountered during pumping. Examples of such approaches are disclosed in U.S. Pat. No. 7,766,812, entitled “Methods and devices for improving mitral valve function,” issued on Aug. 3, 2010, the entirety of which is incorporated herein by reference. One example includes one or more transventricular splints placed across the left ventricle. Each splint may include a tension member extending across the ventricle with anchors disposed on opposite ends of the tension member and placed on the external surface of the heart.
Mitral valve incompetency or mitral valve regurgitation is a common comorbidity of congestive heart failure. As the dilation of the ventricle increases, valve function generally worsens, which results in a volume overload condition. The volume overload condition further increases ventricular wall stress, thereby advancing the dilation process, which further worsens valve dysfunction.
In heart failure, the size of the valve annulus (particularly the mitral valve annulus) increases while the area of the leaflets of the valve remains constant. This may lead to an area of less coaptation of the valve leaflets, and, as a result, eventually to valve leakage or regurgitation. Moreover, in normal hearts, the annular size contracts during systole, aiding in valve coaptation. In heart failure, there is poor ventricular function and elevated wall stress. These conditions tend to reduce annular contraction and distort annular size, often exacerbating mitral valve regurgitation. In addition, as the chamber dilates, the papillary muscles (to which the leaflets are connected via the chordae tendonae) may move radially outward and downward relative to the valve, and relative to their normal positions. During this movement of the papillary muscles, however, the various chordae lengths remain substantially constant, which limits the full closure ability of the leaflets by exerting tension prematurely on the leaflets. This condition is commonly referred to as “chordal tethering.” The combination of annular changes and papillary changes results in a poorly functioning valve.
It can be desirable to provide a therapy which corrects the valve incompetency. A heart with even a small amount of regurgitation may benefit from not only the stress reducing functions of the ventricular splints as described above, but also from an elimination of the regurgitation, which will further off-load pumping requirements of the myocardium.
Surface area of an anchor and/or size of the anchor can correspond to the ability of an anchor to withstand forces due to tension from reshaping the heart and ongoing beating of the heart (although, other design features and material properties may also contribute to the ability of the anchor to withstand tension forces). To be most effective and safe, anchors would ideally be able to withstand high forces, including forces as high as 17 Newtons (N) or higher, while the splint maintains the heart in a desired shape. Further, the anchor should have a large enough surface area to spread out and reduce the pressure on the myocardium. If the pressure gets too high on an area (e.g., a small, focused pressure area) of the heart, this can lead to myocardium necrosis, which can itself lead to migration and sinking of the anchor into the tissue. Accordingly, large anchors, or anchors with a large surface area, may be required, and the larger size/area can make implantation of the anchor difficult and can require opening the heart, chest, and/or sternum, and/or may require other highly invasive procedures.
Currently available methods of mitral valve repair or replacement typically require opening the chest and/or heart, e.g., to gain direct access to the valve and its annulus or another portion of the heart. This type of access typically necessitates a use of cardiopulmonary bypass, which can introduce additional complications to the surgical procedure. Since the implantation of the splints themselves do not require the patient to be on cardiopulmonary bypass, it would be advantageous to devise a technique which could improve the mitral valve without any need for cardiopulmonary bypass. The ability to improve the mitral valve function without the need for cardiopulmonary bypass would be an advantage, both in conjunction with ventricular splinting, and also as a stand-alone therapy. Indeed, it would be desirable to have systems, apparatuses, and methods capable of a deploying an anchor with an ability to withstand high pressures (e.g., an anchor having a large surface area) using a less invasive, or minimally invasive procedure.
Devices and methods for medical treatment that may be used for improving heart valve function are described herein. These may include a self-expandable anchor system and related methods for assisting in treating an apposition of heart valve leaflets so as to improve poorly functioning heart valves, using less invasive treatments/procedures.